The present invention relates to a seat belt retractor.
Seat belt retractors are normally equipped with motive springs that constantly apply force on a seat belt webbing. A seat belt retractor of this type is known from DE 41 12 620. An electric motor in a seat belt retractor adjusts the spring casing of the motive spring to vary the retraction force on the seat belt webbing for improving a vehicle occupant""s comfort. The retraction force is altered by rotationally adjusting an external fixing point of the motive spring. The retraction force is reduced when the seat belt is buckled. When the seat belt is taken off, the external fixing point of the motive spring can be adjusted such that the motive spring exerts an increased retracting force on the webbing.
It is also known for a seat belt retractor to have a pretensioner and a load limiter. One type of pretensioner utilizes a clutch to rotate the belt reel. Pretensioners of this type are disclosed in DE 296 05 200 U1 and DE 196 47 841 A1. A seat belt retractor can also have a load limiter that limits or reduces the load acting on the vehicle occupant during the locking of the belt reel.
The present invention provides rapid removal of slack in a seat belt webbing by a pretensioner. A clutch transmits torque produced by an electrical driving device to the belt reel. The clutch has a spring that can be deformed by torque, and when deformed brings the clutch into an engaged state.
The spring is preferably a wrap spring wherein one end of the spring is connected to the electrical driving device and the other end of the spring is connected to the belt reel. The end of the spring that is connected to the belt reel can be locked into place by a clutch locking mechanism. The clutch locking mechanism is moved by an actuating device to create an interlocking fit with the belt reel. The locking of one end of the spring during production of the torque enables the spring to be deformed by the torque acting on the other end of the spring. The clutch is brought into an engaged state by this deformation.
If the spring is a wrap spring, the cylindrical spring region is deformed radially and is brought directly into a non-interlocking contact, in particular frictional contact, with the belt reel or with a part connected non-rotatably to the belt reel. The torque supplied by the electrical driving device is transmitted directly to the belt reel by this non-interlocking contact.
For transmitting the torque, a driver, that is preferably mounted in a rotatable manner around the belt reel axis, can be arranged between the electrical driving device and the side of the spring onto which the torque is transmitted.
As the torque supplied by the electrical driving device for actuating the clutch initially deforms a spring, abrupt transmission of the torque from the electrical driving device to the belt reel is avoided.
The actuating device for the adjusting element is adjusted to produce the interlocking fit between belt reel and the side of the spring to be held, can act mechanically, electrically, or electromagnetically. The adjusting element is preferably moved radially in relation to the belt reel axis. A lifting magnet can act on the adjusting element for this purpose.
The adjusting element can comprise a bearing for a clutch locking mechanism, with which the interlocking fit between the side of the spring to be held and the belt reel is produced. The clutch locking mechanism is preferably annular in design and is mounted in a rotatable manner. The clutch locking mechanism has internal teeth, which can be engaged with corresponding teeth connected to the belt reel. The clutch locking mechanism can also engage an annular bearing part of one end of the spring. This annular bearing part can also comprise teeth complementary to the internal teeth of the clutch locking mechanism.
The actuating device is activated and torque is supplied to the spring when the probability of a crash is high. Potential crash causing factors include, for example, full braking, skidding of the vehicle, different coefficients of friction on the vehicle wheels in relation to the roadway, the springing out of a wheel or high angular velocity of steering. Situations of this type involving a probability a crash can be detected by appropriate sensors.
When the clutch is engaged the torque produced by the electrical driving device is transmitted to the belt reel for the reversible pretensioning of the seat belt. While the clutch is engaged, the torque supplied by the electrical driving device is maintained for acting on the winding shaft. If no crash occurs the actuating device is deactivated so that the clutch locking mechanism producing the interlocking fit between one side of the spring and the belt reel is disengaged.
The chance of destruction of the load carrying parts during the transmission of torque by the incorporation of a damping device into the seat belt retractor is reduced by the present invention. The damping device, preferably arranged between the electrical driving device and the driver, compensates for the overload between the driver and the electrical driving device, in particular a set of worm gears at the output of the electrical driving device and the driver. This damping device preferably stores energy in the loaded state. This energy can also be used to release the blocking of the belt reel so that the belt reel is on standby for undecelerated extraction of webbing during normal operation.
The present invention also adjusts the retracting force on the seat belt webbing while the seat belt is in use to provide comfort for the vehicle occupant.